Why did the Crusades fail?
The whole campaign lasted from the 1st March 1096 to December 1098. There were more later Crusades, when Poland, Russia and several other nations hoped to follow and do better than the Roman Catholic Church.
It was the greed of the knights, their quench for political and religious power, favoritism that lead to the money running out. It was not the military might and tactics of Muslim Saladin. But in the late stages of the French, English Kingdom of Jerusalem, his forces did act with cunning to rout the Crusaders.
Militarily the Crusaders failed, because they constructed Norman fortresses in the desert with moats, like in Europe and meanwhile there was no water. But ultimately it had to be God. Much is done in Gods name, but it is not of him. It’s just man tagging on his name and hoping for the best, it won’t work, warfare, Church ekklesia, organization, and what ever.
Ask me and I will tell you! 